US3860852A

US3860852A - Fluorescent lamp containing amalgam-forming material

Info

Publication number: US3860852A
Application number: US457927A
Authority: US
Inventors: Frank M Latassa; Howard W Milke; Tadius T Sadoski
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1974-04-04
Filing date: 1974-04-04
Publication date: 1975-01-14
Anticipated expiration: 1992-01-14
Also published as: DE2513332A1

Abstract

A tubular fluorescent lamp having a mount structure sealed in each end comprising a glass stem flared at one end and supporting an emissive coil electrode at the other end. Attached to each mount structure and extending from the electrode region to the flared region is a metal strip carrying an amalgam-forming material, such as a coating of indium. A first region of the amalgam-forming material is located at a higher temperature end of the strip near the electrode for facilitating starting, while a second region of the amalgam-forming material is located at a lower temperature end of the strip near the flare for regulating the mercury vapor pressure of the lamp during operation. The strip may also include means, such as a fin, for minimizing transfer of heat from the electrode to the amalgam-forming material at the lower temperature end of the strip.

Description

United States Patent Latassa et al.

1 1 Jan. 14, 1975 FLUORESCENT LAMP CONTAINING AMALGAM-FORMING MATERIAL Inventors: Frank M. Latassa, Magnolia;

Howard W. Milke, Danvers; Tadius T. Sadoski, Salem, all of Mass.

GTE Sylvania Incorporated, Danvers, Mass.

Filed: Apr. 4, 1974 Appl. No.: 457,927

Assignee:

References Cited UNITED STATES PATENTS Toomey 313/490 Bernier et a1, 313/178 Rasch et a1. 313/178 Evans 313/174 Primary ExaminerRudo1ph V. Rolinec Assistant Examiner'E. R. LaRoche Attorney, Agent, or Firm-Edward 1. Coleman [57] ABSTRACT A tubular fluorescent lamp having a mount structure sealed in each end comprising a glass stem flared at one end and supporting an emissive coil electrode at the other end. Attached to each mount structure and extending from the electrode region to the flared re gion is a metal strip carrying an amalgam-forming material, such as a coating of indium. A first region of the amalgam-forming material is located at a higher temperature end of the strip near the electrode for facilitating starting, while a second region of the amalgamforming material is located at a lower temperature end of the strip near the flare for regulating the mercury vapor pressure of the lamp during operation. The strip may also include means, such as a fin, for minimizing transfer of heat from the electrode to the amalgamforming material at the lower temperature end of the strip.

14 Claims, 3 Drawing Figures PATENTED JAN 1 M975 FIG.3

FIG.2

FLUORESCENT LAMP CONTAINING .AMALGAM-FORMING MATERIAL BACKGROUND OF THE INVENTION This invention relates to low-pressure mercury vapor discharge lamps and more particularly to fluorescent lamps containing an amalgamforming material for regulating the internal vapor pressure.

It is well-known that the light output of a fluorescent lamp is a function of the mercury vapor pressure, which in turn often depends upon the temperature of the coldest region of the glass envelope of the lamp. It is further known that the envelope cold spot temperature for most efficient lamp operation is approximately 40C, which causes a mercury vapor pressure of approximately 4 to 6 X 10 Torr to occur inside the lamp. Often, due to high lamp loading or high ambient temperatures, the envelope temperature and mercury vapor pressure rise above the optimum value.

Various methods of cooling portions of the lamp envelope to regulate vapor pressure have been employed. Shields have been placed between the electrodes and the ends of the envelope; heat sinks have been attached to the envelope; and the lamp envelope has been increased in size, and made with grooves, depressions and the like. It has also been well-known that mercury vapor pressure may be reduced by the use of an amalgam-forming metal, such as cadmium or indium. U.S. Pat. No. 2,966,602 mentions such an application of an amalgam of mercury at column 4, lines 60-64. It has been observed that the location of the amalgam or amalgam-forming metal in the lamp is an important factor in providing the desired improvement in lamp operation. For example, U.S. Pat. No. 3,007,071 discloses the use of an amalgam-forming metal as a strip or powder located along the length of the tubular lamp envelope where it is not exposed to temperatures much higher than those in the discharge. In a lamp described by U.S. Pat. No. 3,392,298, the mercury pressure is controlled by a coating of indium in the form of a ring at the center of the tubular lamp envelope. Such use of an amalgam-forming metal is very effective in fixing the mercury vapor pressure after the lamp reaches thermal equilibrium, but the mercury pressure in the lamp will be extremely low when the lamp is first started since a considerable time is required for the middle part of the lamp, where the indium is located, to warm up. As a result the lamp may only emit a third of its normal light output even two or three minutes after being started, and may not emit its full light output until as long a period as twelve minutes has elapsed.

Accordingly, the use of two sources of amalgam within a fluorescent lamp has been employed-one which heats up rather slowly when the lamp is energized, and then controls the mercury vapor pressure during operation, and a secondary source of amalgam which is located closer to the electrodes and thus heats up at a faster rate and provides a sufficient amount of mercury vapor to enable the lamp to reach its output more rapidly. A fluorescent lamp of this type is disclosed in U.S. Pat. No. 3,227,907. According to this patent, the cool spot deposit of amalgam-forming material is provided by a band of indium at the center of the glass tube as described in U.S. Pat. No. 3,392,298, and the hot spot deposit of indium is located on auxiliary electrodes, such as flag anodes, connected to the cathode coil lead-in wires. Such auxiliary electrodes generally rise quickly in temperature, and may reach temperatures as high as 300C and 400C. Whatever mercury is picked up by the indium in this location will be quickly vaporized into the atmosphere of the lamp and quickly diffused through it.

Although the above-discussed cool spot locations of amalgam, viz., a lengthwise strip or deposit of amalgam-forming metal or a center band of indium, can provide effective pressure regulation, it is difficult to apply the amalgam with sufficient adherence at such locations on the interior surface of the lamp envelope, and it complicates manufacture of the lamp since portions of the lamp have to be cooled during the exhaust and baking operations in order to prevent the amalgam from melting and flowing away from the desired location. In addition, some amalgam-forming metals or amalgams have such a low melting point that they become liquid at the operating temperatures within the lamp and thus create a situation where the amalgam may not remain at the desired location within the lamp. Further, the use of an amalgam center band of lengthwise strip will block radiation and thus cause in appearance defect and some loss of light output, which may be objectionable in specific applications. Also, amalgam locations toward the center of the lamp envelope are more sensitive to ambient temperature and thereby cause shifts in the mercury control point of the lamp.

According to one approach for overcoming the above-mentioned disadvantages of prior cool spot locations of amalgam for providing the main vapor pressure control means within the lamp, a strip of the amalgamforming metal is placed in a wire mesh holder which is wrapped and tied or clamped about the cylindrical portion of the glass mount stem at one or both ends of the lamp envelope. The temperature of the amalgam during lamp operation is dictated by the length of the stem and the selected axial position of the mesh wrap along the stem (and thus its distance from the electrode). Such a structure is described in the following U.S. Pats. Nos. 3,373,3033,442,299; 3,526,802; 3,526,804; 3,534,212; and 3,619,697. A disadvantage of this approach is that is complicates the lamp making process by the additional manual or mechanical steps required to properly place the indium into the wire mesh and attach the mesh about the mount. Also, this limited temperature location of the amalgam-forming metal, i.e., in a wire mesh wrapped about the barrel of the mount stern, compromises optimization of vapor pressure control over the starting, warm-up and operating phases of the lamp cycle.

In another approach to overcome the disadvantages of prior cool spot locations of amalgam for providing the main pressure control means in a fluorescent lamp, U.S. Pat. 3,548,241 describes a method whereby a suitable amalgam-form'ing metal, such as indium, is heated to the liquid state and then sprayed onto the flared portion of one of the glass mount stems before it is sealed into the envelope. The spray is controlled to deposit a band of the amalgam-forming metal having a thickness of less than microns which extends around the circumference of the flared portion of the stern. Starting is facilitated by an auxiliary (hot spot) source of amalgam secured to an electrode cap (disintegration shield). Another reference, viz., U.S. Pat. No. 3,629,641 describes a fluorescent lamp containing amalgams at three different locationsthe main amalgam location is a spray deposit of indium on the stem flare; the hot spot amalgam location is a strip of indium alloy on the electrode cap; and the third and intermediate pressure control location comprises a spot of indium on the stem press. Although optimizing vapor pressure control over the starting and operating phases of the lamp cycle, the provision of two or more distinct depositions of indium on the lamp mount introduces added complications to the fabrication of the lamp, thereby adversely affecting cost. Further, difficulty is experienced in obtaining a good indium-to-glass bond, since indium does not readily flow or wet over nonmetallic surfaces.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an improved low-pressure mercury vapor discharge lamp.

A principal object of the invention is to economically provide an electric discharge lamp with an improved mercury-vapor pressure control means.

A particular object is to provide an improved fluorescent lamp containing an amalgam or amalgam-forming metal in a manner which optimizes mercury-vapor pressure control over the starting and operating phases of the lamp cycle yet simplifies fabrication.

These and other objects, advantages and features are attained, in accordance with the principles of this invention, by supporting the amalgam-forming material on an elongated carrier which is attached to one of the lamp mount structures and extends from the electrode region thereof toward the opposite end of the stem forming a part of that mount. The amalgam-forming material is disposed on the carrier such that a first region thereof is located at the end of the carrier near the electrode, to thereby have a higher operating temperature for facilitating starting of the lamp, and a second region of the amalgam-forming material is located at the opposite end of the carrier to have a lower operating temperature for regulating the mercury vapor pressure during lamp operation. In order to minimize the transfer of heat from the electrode to the opposite end of the carrier, where the second region of amalgamforming material is located, a heat-shield fin may be formed from the carrier between the first and second regions of amalgam-forming material, or the carrier may be shaped to have a narrowed neck portion between these regions.

According to one particular embodiment of the invention, as applied in a tubular fluorescent lamp having a flared stem sealed at each end supporting an electrode structure including a cathode coil with anode probes, the carrier comprises a thin strip of iron welded to an anode probe at each end of the lamp and extending from the electrode to the stem flare. The amalgamforming material on each strip comprises a first patch of indium disposed near the end of the strip attached to the anode probe and a much larger quantity of in dium disposed at the end of the strip near the stem flare. Hence, a simply attached, single carrier provides both hot and cool spot deposits of indium for obtaining the dual functions of faster starting and maintenance of the desired operating vapor pressure. The indium can be applied to the carrier separately from the existing manufacturing equipment and then merely welded to an anode probe or otherwise clamped to the mount structure, thereby significantly simplifying the manufacture of amalgam-type fluorescent lamps having two-phase vapor pressure control.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a fluorescent lamp is shown com- 1 prising an elongated tubular glass envelope 10 having the customary coating 11 of phosphor on its inner surface and electrode mounts l2 sealed into each of its ends. The light-transmitting envelope is filled with a small amount of rare gas, such as argon, at low pressure, e.g., l to 3 Torr, and a small quantity of mercury, say 50 mgs. after which it is hermetically sealed in the usual manner by tipping off the exhaust tube 25 (see FIGS. 2 and 3) at one of both ends of the lamp.

Each mount structure 12 includes the typical reentrant vitreous stem 13 having at one end a flared portion 14, which is sealed about its periphery to the end of the tubular glass envelope, and a press 15 at the inward end supporting an electrode arrangement 16. More specifically, the electrode comprises a cathode coil 17, (see FIGS. 2 and 3) preferably consisting of a coiled tungsten filament carrying the usual alkalineearth oxide (electron-emissive) coating, supported on a pair of

lead wires

18 and 29 sealed through the stem press 15 and extending to

terminal pins

20 and 21 insulatively mounted in the lamp bases 22 attached to each end of the hermetically sealed, light-transmitting envelope 10. A pair of metal anode probes 23 and 24 are also mounted on either side of and in parallel relationship with the cathode coil 17, preferably by attaching them to the ends of the lead wires.

The lamp of FIG. 1 further includes a mercury vapor pressure control means according to the invention which, in this particular embodiment, includes an elongated solid strip 26 of metal, e.g., iron, which is attached at one end, such as by welding, to the anode probe 23 and extends from the electrode region to the opposite end of the stem 13, i.e., to the region of the flare 14, as illustrated. Additionally, the strip 26 may be clamped to the stem 13 by means of a strap or spring clip 28. The metal strip 26 serves as a carrier for an amalgam-fonning material 27, such as indium, which is coated along the full length of one surface of the strip 26. In this manner, a first region 27a of the amalgamforming material is located at the end of the carrier strip 26 near the thermionic cathode coil, which becomes quite hot during lamp operation, while a second region 2711 of the amalgam-forming material is located at the opposite end of the carrier strip 26 near the much cooler flare portion 14 of the stem 13.

In operation, an alternating current is applied across the lamp electrodes sustaining an arc therebetween through the mercury vapor within the envelope, thereby causing the vapor to emit ultraviolet light which excites the phosphor coating 11 to fluorescence, particularly along major portions of the lamp between the electrodes. During operation at high ambient temperatures or high lamp loadings, the lamp temperature will rise and the mercury vapor pressure increases. If the vapor pressure were uncontrolled, it would soon exceed an optimum value (4 to 6 microns) and light output would drop off.

In accordance with the present invention however, location of a substantial amount of, say, indium 27 at the cooler region (27b) of the carrier strip 26, which is typically at a temperature between 80 to 100C during lamp operation, causes more mercury to condense and amalgamate with the indium than would do so in hotter portions of the lamp, and thus makes it possible for the indium to control the mercury vapor pressure by holding it at or near the optimum value (4 to 6 microns) for high light output. Further, it makes such control possible without the necessity of forced ventilation. Manufacture of the lamp is simplified by applying the indium to a metal carrier attached to the mount, rather than to the inside wall of the envelope or as a spray coating on the stem, whereby complications would be introduced directly into the lamp fabrication process. It is also assured that, after lamp operation, mercury will condense at the lamp ends, rather than on the phosphor of the major illumination portions of the lamp.

If all the indium were at the cooler region 27b, however, the lamp would not emit much light for a period of several minutes after starting. The delay is due to the time necessary to heat the indium of region 27b to a temperature sufficient to give high enough mercury vapor pressure, since the indium reduces the pressure. However, at the higher temperature region 27a, the indium is quickly heated by the radiation from the filament coil 17 and indirectly by the electric current picked up by the anode probe 23, so that the mercury vaporizes and leaves the indium for the interior of the lamp. The indium, however, is not readily volatilized because of its lower vapor pressure and higher melting temperature, so it remains at region 27a on the carrier strip 26. Hence, the higher operating temperature of indium region 27a facilitates lamp starting and significantly reduces warm-up time, while the cooler region 27b of indium function as the main regulator of mercury vapor pressure during lamp operation.

As the lamp cools on being turned off, the indium region 27a absorbs mercury, the amount of mercury present being shared with indium region 27b during the of equilibrium state, that is, when the power is not connected to the lamp. Preferrably, the quantity of indium at region 27a is made small so that the amount of mercury present in the lamp will not have to be greatly increased to maintain the proper amount at region 27b.

Again, manufacture of the lamp is simplified by applying both the hot and cool spot locations of amalgamforming material (27a and 27b) on a single metal carrier attached to the lamp mount, rather than at two or more locations on the lamp envelope, stem, and/or electrode elements, whereby significant alteration would be required in the normal manufacturing operation for fabricating the lamp mount and the tubular lamp envelope. Further, the coating, deposition, or insertion of amalgam-forming material on a separate carrier to be attached to the lamp mount provided a much more controllable process for accurately disposing indium, or the like, into the lamp.

FIG. 2 illustrates the lamp mount 12, prior to installation, with an alternative embodiment of the vapor pressure control means attached thereto. In this instance the carrier strip is formed of a metal wire mesh 29, which is attached to the mount structure solely by welding the upper end of the mesh strip to the anode probe 23. The hot and cool regions of amalgamforming material comprise two separate patch coatings 30a and 30b, respectively, on one side of the mesh carrier 29, as illustrated. A heat-shield fin 31 is formed from the metal mesh carrier to project approximately normal to the main portion thereof at a point between the coating regions 30a and 30b for minimizing the transfer of heat from the cathode coil 17 to the opposite end of the carrier 29, where the region 3012 of amalgam-forming material is located. More specifically, the fin arrangement reduces heat transfer by radiation as well as by providing a larger surface area to emit heat by radiation or convection. Thus, for example, a small amount of indium coated, impregnated, or inserted at region 30a on the mesh carrier 29 will be heated rapidly by the cathode coil 17 to facilitate starting, while a larger quantity of indium located at the cooler region 30b will provide the main source of mercury-vapor pressure regulation during lamp operation, the heatshield fin 31 contributing toward maintaining the desired lower temperature at region 30b.

The mesh carrier 29 can be formed by any of a number of materials, provided the material is substantially inert with respect to both mercury and the amalgamforming metal, does not decompose in the lamp environment, and is a material which the amalgam will wet. Accordingly, the mesh can be made from glass or quartz fibers or from iron nickel, nickel plated iron, aluminum, titanium, steel or stainless steel wire. Further, any suitably foraminous material, such as perforated sheets of metal, can also be used in place of metal cloth strips. Alternatively, a foam metal may be employed as the carrier strip.

FIG. 3 illustrates another alternative embodiment of the invention wherein the carrier comprises a solid strip 32 of metal attached at one end to anode probe 23 and having a narrowed neck portion 33 between two separate regions 34a and 34b of amalgam-forming material coated on opposite ends of the strip 32. The neck 33 reduces the transfer of heat from the cathode coil 17 to the cooler region 34b of amalgamforming material.

According to one specific embodiment, the mount structure of FIG. 3 is employed at both ends of a 40 watt fluorescent lamp having an argon fill at 2.5 Torr and containing 50 mgs of mercury. Each carrier 32 comprises a strip of iron A inch wide, 1% inches long and 5 mils thick, with a neck 3/32 inch wide and inch long. About 5 mgs. of indium is coated on each carrier at region 34a, and about mgs, of indium is contained at the cooler region 34b of a carrier at each end of the lamp. As a result of the hot spot location of indium at 34a, the lamp reached of light output approximately 60 seconds after ignition, and as a result of the cool spot location of indium at 34b, the lamp produced a relative light output of not less than 90% over an ambient temperature range from approximately 45F to l35F as compared to a non-amalgam 40 watt lamp wherein the 90% relative light output spread was only 55F, i.e., from about 45F to 100F.

The metal carrier strips 26 or 32 may be formed of iron, steel, nickel, stainless steel, aluminum or titanium. Other amalgam-forming metals, such as cadmium, may be employed. The carrier may be attached to one or both lamp mounts by welding or clamping to a probe or inner lead. It could also be attached to a post not electrically connected to the coil. The amount of amalgam-forming material at the hot region (viz., 27a, 30a or 34a) may range from approximately 3 to milligrams, and the total amount of amalgam-forming material in the cooler regions (viz., 27b, b or 34b) on all carriers in the lamp should have a weight ratio to the mercury in the lamp of from about 2:1 to 12:1.

Hence, although the invention has been described with respect to specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the true spirit and scope of the invention. What we claim is:

1. A low-pressure mercury vapor discharge lamp comprising:

an hermetically sealed, elongated light-transmitting envelope containing an inert ionizable fill gas and a quantity of mercury,

a mount structure including a stem sealed to and extending inwardly from each end of said envelope and an electrode supported at the inward end of each of said stems,

at least one of said mount structures having attached thereto an elongated carrier extending from the electrode region thereof toward the opposite end of the stem thereof, and

an amalgam-forming material contained on said carrier, a first region of said amalgam-forming material being located at the end of said carrier near said electrode to thereby have a higher operating temperature for facilitating starting of said lamp, and a second region of said amalgam-forming material being located at the opposite end of said carrier to thereby have a lower operating temperature than said first region for regulating the mercury vapor pressure of said lamp during operation.

2. A lamp according to claim 1 wherein said carrier comprises an elongated strip of metal coated with said amalgam-forming material.

3. A lamp according to claim 1 wherein said carrier is foraminous.

4. A lamp according to claim 1 wherein: each of said mount structure stems if formed of a vitreous material. and said carrier is made of a material selected from the group consisting of iron, steel, nickel, stainless steel, aluminum, titanium, a mesh of glass fibers or a mesh of guartz fibers.

5. A lamp according to claim 4 wherein said amalgam-forming material is indium.

6. A lamp according to claim 1 wherein said elongated carrier includes means for minimizing the transfer of heat from said electrode to the opposite end of said carrier where said second region of amalgamforming material is located.

7. A lamp according to claim 6 wherein said means for minimizing heat transfer comprises a heat-shield fin formed from said carrier to project approximately normal to the main portion thereof at a point between said first and second regions of amalgam-forming material.

8. A lamp according to claim 6 wherein said means for minimizing heat transfer comprises a narrowed neck portion of said carrier between said first and second regions of amalgam-forming material.

9. A lamp according to claim 1 wherein said elongated carrier is attached to said stem of said mount structure.

10. A lamp according to claim 1 wherein said elongated carrier is metal and is attached at one end to the electrode supported by said mount-structure and thereby electrically connected to said electrode.

11. A lamp according to claim 10 wherein said electrode comprises a cathode coil with anode probes attached thereto, and said one end of the carrier is attached to one of said anode probes.

12. A lamp according to claim 11 wherein said carrier is also clamped to the stem of said mount structure.

13. A lamp according to claim 1 wherein said first and second regions of amalgam-forming material comprise two separate patch coatings thereof on said carrier.

14. A lamp according to claim 13 wherein the amount of amalgam-forming material in the first region thereof on each carrier in said lamp is approximately 3 to 10 milligrams, and the total amount of amalgamforming material in the second regions thereof on all carriers in said lamp has a weight ratio to the mercury in said lamp of from about 2:1 to 12:1.

Claims

1. A LOW-PRESSURE MERCURY VAPOR DISCHARGE LAMP COMPRISING: AN HERMETICALLY SEALED, ELONGATED LIGHT-TRANSMITTING ENVELOPE CONTAINING AN INERT IONIZABLE FILL GAS AND A QUANTITY OF MERCURY, A MOUNT STRUCTURE INCLUDING A STEM SEALED TO AND EXTENDING INWARDLY FROM EACH END OF SAID ENVELOPE AND AN ELECTRODE SUPPORTED AT THE INWARD END OF EACH OF SAID STEMS, AT LEAST ONE OF SAID MOUNT STRUCTURES HAVING ATTACHED THERETO AN ELONGATED CARRIER EXTENDING FROM THE ELECTRODE REGION THEREOF TOWARD THE OPPOSITE END OF THE STEM THEREOF, AND AN AMALGAM-FORMING MATERIAL CONTAINED ON SAID CARRIER, A FIRST REGION OF SAID AMALGAM-FORMING MATERIAL BEING LOCATED AT THE END OF SAID CARRIER NEAR SAID ELECTRODE TO THEREBY HAVE A HIGHER OPERATING TEMPERATURE FOR FACILITATING STARTING OF SAID LAMP, AND A SECOND REGION OF SAID AMALGAM-FORMING MATERIAL BEING LOCATED AT THE OPPOSITE END OF SAID CARRIER TO THEREBY HAVE A LOWER OPERATING TEMPERATURE THAN SAID FIRST REGION FOR REGULATING THE MERCURY VAPOR PRESSURE OF SAID LAMP DURING OPERATION.

3. A lamp according to claim 1 wherein said carrier is foraminous.

4. A lamp according to claim 1 wherein: each of said mount structure stems if formed of a vitreous material, and said carrier is made of a material selected from the group consisting of iron, steel, nickel, stainless steel, aluminum, titanium, a mesh of glass fibers or a mesh of guartz fibers.

5. A lamp according to claim 4 wherein said amalgam-forming material is indium.

6. A lamp according to claim 1 wherein said elongated carrier includes means for minimizing the transfer of heat from said electrode to the opposite end of said carrier where said second region of amalgam-forming material is located.

14. A lamp according to claim 13 wherein the amount of amalgam-forming material in the first region thereof on each carrier in said lamp is approximately 3 to 10 milligrams, and the total amount of amalgam-forming material in the second regions thereof on all carriers in said lamp has a weight ratio to the mercury in said lamp of from about 2:1 to 12:1.